1. Field of the Invention
The present invention relates in general to medical lasers and in particular to a dental laser method and apparatus for performing surgical procedures involving the soft tissues, teeth and bone in the oral cavity.
2. Description of the Prior Art
The procedures dentists perform in the oral cavity usually involve either correcting diseases or defects of soft tissues, for which scalpels and similar surgical instruments are used, or for correcting diseases of the hard tissues, such as enamel and dentin of the teeth, for which mechanical drills are used. In addition, for some procedures, such as certain periodontal surgical procedures, and for removal of impacted wisdom teeth, removal of bone is also involved, usually by mechanical drills, chisels and the like. All these procedures usually cause discomfort to the patient.
In recent years, dental lasers have been used by dentists. Two kinds of lasers, the Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) and the Carbondioxide (CO2) lasers have been used by dentists, but only for soft tissue surgery in the mouth. Another kind of laser, the Argon laser, is used by dentists mainly for polymerization of certain kinds of materials used for filling cavities. However, studies have shown that what patients undergoing dental treatment dislike most are the grinding sensation and the whirring noise of the mechanical drills used by the dentist for drilling teeth. Many patients avoid timely dental care out of fear of the mechanical drills. Neither the Nd:YAG, CO2 or Argon lasers can be used for drilling of teeth, for reasons that will be shown below.
U.S. Pat. No. 4,521,194 to Myers et al disclosed a method for removing incipient decay from teeth and U.S. Pat. No. 4,818,230 to Myers et al disclosed a method for removing decay from teeth. Both the above-mentioned patents disclosed the use of a Nd:YAG laser for removing the decay by exposing the decayed dentin of the tooth to the laser. However, the currently acceptable method in dentistry of treating tooth decay involves removal of not just the decayed dentin of the teeth as is taught by the above-mentioned patents but rather also involves removal of the surrounding sound, healthy, intact enamel at the margins of the decayed area. This is intended to ensure that when the cavity is filled, the margins of the filling will be so shaped and situated as to ensure success of the completed filling. Therefore, for a laser to be useful for drilling teeth, that laser would also have to be able to cut sound enamel and dentin and not just remove decayed dentin. Neither the Nd:YAG nor the CO2 lasers have been shown in studies to cut sound, intact enamel and dentin without causing structural damage to the tooth and without heating the tooth pulp to temperatures that would cause irreversible pulp damage. Therefore, the lasers and methods disclosed in the above-mentioned patents cannot be utilized for cutting hard tooth tissue, and dentists still have to use the mechanical drill.
U.S. Pat. No. 4,940,411 to Vassiliadis et al disclosed a dental laser assembly capable of removing decayed portions of teeth, capable of desensitizing teeth and removing soft tissues. However, their invention also could not remove sound, healthy intact enamel. Therefore a dentist using their laser assembly would still have to use a conventional, mechanical drill to accomplish restoration of tooth decay.
U.S. Pat. No. 5,020,995 to Levy also disclosed that decayed tooth tissue can be cut with a Nd:YAG laser; and that if the Nd:YAG laser would be used to cut healthy tooth tissues such as healthy, intact enamel and dentin, a dark spot would first have to be formed at the portion to be cut, by applying graphite from a lead pencil onto the tooth. However, the graphite would be applied to only the most superficial layer of enamel, and once that superficial layer of enamel was cut with the laser, the graphite would have to be reapplied and when that layer was cut the dentist would have to stop the laser and reapply the graphite. Therefore, to complete the cutting process, repeated stoppage and reapplication of the graphite would be necessary and that would be awkward and inconvenient and not practical. The repeated application of graphite on a tooth in a patient's mouth would also pose a health hazard to the patient; in addition, plume resulting from the interaction of the laser with the graphite on a patient's tooth may pose an additional risk to dentist and patient.
Recent studies have shown that laser energy radiating at certain other wavelengths is considerably better suited for cutting sound dental enamel and dentin. In particular, the pulsed Erbium:Yttrium-Aluminum-Garnet (Erbium:YAG) laser, having a wavelength of 2.94 microns, has been shown to not only remove decay but also cut sound enamel and dentin without causing structural damage to the tooth and without causing temperature rise of the tooth pulp beyond the 5 degrees C. threshold for irreversible pulp damage. Therefore, for treating decayed teeth, the Erbium:YAG laser can be used not only to remove the decayed part of the tooth but also to cut the healthy enamel and dentin at the margins of the decayed portion for acceptable cavity restoration. In addition, the Erbium:YAG laser can also be used to cut the intact enamel and dentin overlying the tooth pulp chamber so as to get access to the root canal to initiate root canal therapy. None of the lasers of the prior art teaches cutting enamel and dentin with a laser to get access to the pulp chamber to initiate root canal therapy. The Erbium:YAG laser can also be used to section the roots of teeth in root resection surgical procedures.
The Erbium:YAG laser has also been shown to be very effective for soft tissue surgical procedures due to its very high absorption in the cellular fluids of the soft tissues as compared to both the CO2 laser and the Nd:YAG laser. The 2.94 micron Erbium:YAG laser output coincides with the major water absorption band which peaks around 3.0 microns. In fact, the absorption of the Erbium:YAG laser in water is ten times greater than the absorption of the CO2 laser in water and almost 20,000 times greater than the absorption of the Nd:YAG laser in water. When laser energy is absorbed by the water in the cells in the body, laser light produces an intense thermal reaction which leads to vaporization of the cellular contents and eventual disruption of the cells. If a laser is very highly absorbed by the cellular fluids, its cutting efficiency is high, the resultant surgical incision has a narrower zone of thermal damage around it and post-operative healing is better.
The high water absorption of the Erbium:YAG laser is also believed to be responsible for the efficient cutting of enamel and dentin with the Erbium:YAG laser.
Moreover, the Er:YAG laser has also been shown in studies to be capable of cutting bones without causing necrosis of the bone cells.
Thus it would appear that the Er:YAG laser is one laser that could be used by the dentist for soft tissue, hard tissue and bone removal procedures. However, the Er:YAG laser has not found application in dental practice. This is because the Er:YAG laser has, until now, lacked an adequate delivery system to convey the laser energy from the laser head, where the laser energy is generated, to the patient's mouth. Silica optical fibers, which are so successful in conveying the laser energy in dental lasers of the prior art, such as the Nd:YAG laser, cannot conduct laser radiation beyond wavelength of approximately 2.5 microns. Therefore, silica fibers cannot convey erbium laser radiation having a wavelength of 2.94 microns. Certain other types of fibers have been tested, including zirconium fluoride fibers, but they have not been demonstrated to be successful for delivery of the Er:YAG energy without loss of energy, fracture of the fiber and/or damage to the tip of the fiber during operation. An articulated arm arrangement is typically used, connecting the laser head, where the laser energy is generated, to a hand- held tool to be used in the patient's mouth. However this articulated arm is usually bulky and awkward for surgical application in the mouth.
In U.S. Pat. No. 5,055,048, Vassiliadis et al, while disclosing a Nd:YAG dental laser, state in the specifications that an Erbium doped YAG laser has proven effective for removal of enamel. However, they too admit that at present, Erbium:YAG lasers are destructive to optical fibers of the type used their laser system, where the laser radiation is generated in a housing and is then conveyed through the optical fiber to the tissues in the patient's mouth. They, too, do not claim that their Nd:YAG laser is capable of cutting sound, healthy enamel.
What has been needed has been a method of removal of soft tissues, hard tissues and bone in the oral cavity which takes advantage of the high tissue absorption of the Er:YAG laser without the inconvenience and problems associated with an inefficient fiber or an articulated arm. Further, what has been needed has been an apparatus for application of the needed method.